Effect of honeycomb porous plate on critical heat flux in saturated pool boiling of artificial seawater

Abstract

During a severe nuclear power plant accident, the integrity of the reactor pressure vessel must be assured. In response to a possible fuel meltdown, operators of the current generation of nuclear power plants are likely to inject water into the reactor pressure vessel to cool down the reactor vessel wall, preserving its integrity and avoiding leakage of radioactive material. This study considers the use of seawater to flood a reactor pressure vessel combined with the attachment of a honeycomb porous plate (HPP) on the vessel outer wall as a way to improve the safety margins for in-vessel retention of fuel. In long-duration experiments, saturated pool boiling of artificial seawater was performed with an upward-facing plain copper heated surface 30 mm in diameter. The resulting value for critical heat flux (CHF) was 1.6 MW/m 2 at atmospheric pressure, a value significantly higher than the CHF obtained when the working fluid was distilled water (1.0 MW/m 2). It was verified that sea-salt deposits could greatly improve surface wettability and capillarity, enhancing the CHF. The combination of artificial seawater and an HPP attached to the heated surface improved the boiling heat transfer coefficient and increased the CHF up to 110% (2.1 MW/m 2) as compared to distilled water on a bare surface. After the artificial seawater experiments, most of the wall micropores of the HPP were clogged because of sea-salt aggregation on the HPP top and bottom surfaces. Thus, the CHF enhancement observed in this case was attributed mainly to the separation of liquid and vapor phases provided by the HPP channel structure and improvement of surface wettability and capillarity by sea-salt deposition.

Effect of grooves on nucleate boiling heat transfer from downward facing hemispherical surface

“…Various methods have been proposed for enhancing ERVC performance, including using structured surface, nanofluids (Pham et al, 2012;Angayarkanni and Philip, 2015) and thermal insulation (Yang et al, 2005;Noh and Suh, 2013). The structured surfaces include porous coating (Yang et al, 2006;Jun et al, 2016;Tetreault-Friend et al, 2016;Sohag et al, 2017;Wang et al, 2018), pin fins (Chu et al, 2013;Zhong et al, 2015), micro channels (Bai et al, 2016;Hou et al, 2017;Zhong et al, 2018aZhong et al, , 2018b, honeycomb porous plates (Mt Aznam et al, 2016;Fogaça et al, 2018), and spherical porous bodies (Mori et al, 2018), and so on. Yang et al (2006) fabricated a downward facing hemispherical surface with micro-porous coatings by sintering, while Sohag et al (2017) developed a Cold Spray technique to coat the same scale surface, both the coating surfaces were tested in the SBLB (Sub-scaled Boundary Layer Boiling) facility to investigate the CHF.…”

“…Mt Aznam et al (2016) investigated the CHF enhancement in combination with surface modification by attaching honeycomb porous plate (HPP) and nanoparticle deposition; the CHF of plain surface increases from 0.13 to 0.98 MW/m 2 with the inclination angle changing from 10° to 180°, while the CHF of structured surface was 1.51 to 1.75 MW/m 2 when the angle increased from 10° to 180°. Effect of HPP on CHF in saturated pool boiling of artificial seawater was studied by Fogaça et al (2018). They concluded that the CHF enhancement by HPP and nanoparticle deposition was the role of capillary action.…”